This invention relates to a method of fault diagnosis based on a propagation model, specifically, it relates to a method for diagnosing a fault by using, as observed information, a time-series of alarms.
Regarding a fault diagnosis of a transmission line, prior art will be described.
The transmission line is composed of tandem connected multiplexer and/or terminating sets etc. For monitoring the transmission line system. ITU-T series G recommendations prescribe how to generate an alarm in each device which composes the system.
According to the alarm generation method prescribed by the ITU-T series G recommendations, when a communication is stopped by a fault at arbitrarily one point within the transmission line system, alarms are notified to a monitoring apparatus from all of the devices which detected the stop of communication. Therefore, accordingly as an affect of the fault is spread in the communication line system, the number of alarms, which are notified to and arrived at the monitoring apparatus, increases.
It is necessary to consider the following states (1) and (2) for executing, by using such alarm, a fault diagnosis in the transmission line.
(1) There exist a time delay in alarm propagation and a time delay in alarm detection, and these are not constant. Then, an order of alarm, observed by the monitoring apparatus, is not constant.
(2) There are plural fault hypotheses, which cause the observed alarm. Therefore, it may be not possible to decide whether only one fault has occurred and spread over the communication line or plural faults were simultaneously occurred.
In a prior art of fault diagnosis based on alarm of which observation order is not stable or constant, It is generally to collect a set of alarms within a time window after a fault occurred, and to decide the most probable fault hypothesis which explains the set of alarms within the time window.
However, the prior art is not able to select the most probable fault hypothesis when there is a loss in the observed data. Then, in the prior art, it is necessary to decide a priority between the hypotheses by a try and error manner.
An object of the present invention is to provide a method of fault diagnosis which can minimize the necessary time for observing alarms without a lack of precision.
Another object of the present invention is to provide a method of fault diagnosis which can estimate the most probable fault portion even if there is a loss in the observed alarm data.
For solving these objects and performing a fault diagnosis in the present invention, a fault hypothesis is expressed by a time-series model based on an alarm propagation model, and a problem for selecting the fault hypothesis is changed to a problem for judging a likelihood of the time-series model.
In a preferred embodiment, the present invention is directed to a method of fault diagnosis based on using, as an observed information, a model of alarm propagation comprising the steps of:
presuming a fault hypothesis as a time-series model prescribed by a parameter of time delay;
defining a likelihood of the fault hypothesis by a product of a probability density of an observation delay time about alarm which is observed at a fault occurrence;
deciding the most probable fault hypothesis by comparing likelihood between the observed alarm time-series and the fault hypotheses; and
estimating a fault portion based on the decision.
In a further preferred embodiment, the present invention is directed to a method further comprising the steps of:
obtaining AIC (Akaike""s Information-theoretic Criterion) of each fault hypothesis;
arranging the fault hypotheses in order of small AIC; and
identifying, as the most probable fault hypothesis, the fault hypothesis whose AIC is the minimum.
In a still further preferred embodiment, the present invention is directed to a method further comprising the steps of:
constructing a fault tree of which node corresponds to each device and of which link corresponds to each connection between the devices;
defining a probability distribution and a probability density function of the observation delay time of alarm, by giving alarm detection delay to each node and giving alarm propagation delay to the link,
respectively as alarm delay parameter associated with a route of the fault tree;
estimating, before alarm arrival, a likelihood of the fault hypothesis at a time t when alarm is observed, by the probability density function;
defining, after alarm arrival, as the likelihood of the fault hypothesis at the time t when alarm is observed, a value of the probability density function when alarm arrived; and
defining the likelihood of each fault hypothesis by the product of the probability density function of the occurred alarm.
The objects of the present application will become more readily apparent from the detailed description given hereafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.